Heated lunch boxes of the abovementioned type are generally known in the art. Examples of such are shown in U.S. Pat. Nos. 3,482,078 to Milne and 3,869,595 to Collins et al. Each of these patents provide a lunch box with a heating element therein for heating the contents of the container when desired. Each of the abovementioned patents disclose a portable lunch box wherein heating elements are provided for heating a fluid such as water thereby creating a vapor for heating the food positioned within a tray. It should be noted however, that with the abovementioned lunch box the food contained therein is positioned in a single tray or compartment such that only food which is to be heated can be placed in these trays. Further, the food within the lunch box is not subjected to any cooling while placed therein and depending upon the particular food, this food may spoil prior to its consumption by the user. Further, in the lunch box of U.S. Pat. No. 3,482,078 extensive seals must be provided between the chamber containing the liquid and the rest of the lunch box, such that none of this fluid is lost during transportation of the box. As to the lunch box illustrated by U.S. Pat. No. 3,869,595, vents are provided for venting the vapor during use of the box. Therefore, the water contained in the lower portion of the lunch box can only be applied thereto when the box is ready for use. Otherwise, if the box were to be upset during its lunch box water would leak from the vents provided in the upper portion of the lower chamber.
In an attempt to solve the aforementioned problems, U.S. Pat. No. 4,630,671 issued to Sherman et al. discloses lunch box body having a vessel mounted therein which is filled with a freezable liquid to cool the interior of the lunch box prior to its use. However, this vessel is permanently mounted on a cover portion of the lunch box and therefore must always be carried with the lunch box in either the frozen or unfrozen state, thereby unnecessarily adding to the overall weight of the lunch box. Further, the food to be heated in the lunch box of this type is merely placed in the heated chamber 4 which is directly heated by the heating element. Such direct contact between the food and the heating element is often undesirable in that the portion of the food closest to the heating element will heat the fastest while leaving other portions of the food unheated or a portion of the food closest to the heating element may become burned prior to the sufficient heating of the portion of food away from the heating element.
Clearly, there is an outstanding need for an improved lunch box wherein the food is conveniently contained in individual containers and may be steam heated when desired by the user. Further, there is a need for a lunch box which can be selectively cooled, with the cooling medium being ultimately used as the source of steam for heating the food contained therein.